Ethylene acrylic acid (EAA) is a ubiquitous substance with wide-ranging uses in industry and commerce. Among these multiferous uses is its incorporation into an aqueous dispersion after batch reaction for diverse coating and like purposes, as are well known in the art.
Aqueous dispersions have significant advantages when used in the coating arts as compared to the common use of organic solvent dispersions and solutions, especially with respect to environmental, fire/explosive hazards, and pollution factors of organic volatiles and the significant difficulty and cost of collecting and satisfactorily handling the same during application and curing of the coatings.
On the other hand, as noted further hereinafter, aqueous-based EAA coating materials, as heretofore available, have relatively high water content, which while explosive-safe and fume safe, require excessive and often unacceptable drying times, whereby in weighing the practical and economic merits of one against the other, the environmentally undesirable organic-based coatings have necessarily remained in widespread usage despite the increasing inveighment thereagainst.
Such prior art teachings as to high mole ratio EAA dispersions are illustrated by the Dow Chemical patent to McCann et al U.S. Pat. No. 3,799,901, the teachings of which are incorporated herein by reference. With respect to the Dow patent teachings as well as to present and indeed heretofore long-term availability of EAA aqueous dispersions, such dispersions are readily commercially available at 35% and 25% EAA solids proportion. The starting EAA bead resin therefor is available from various suppliers, including Dow Chemical Company under the trademark "Primacor" adhesive polymer utilizing beads identified as "5980"or "5990". Such beads are available in ammonia dispersions, as those known as "ADCOTE" of Morton Thiokol Chemical Corporation, with 25% EAA solids proportion using Dow Chemical "5980" beads (high molecular weight) or with 35% EAA solids using Dow "5990" beads (low molecular weight). In like manner, "YUKALON" EAA resin is available from Mitsubishi Chemical Corporation and is comparable to the Dow "5980" resin, while Dow Chemical itself has marketed "Primacor 4983 dispersion using the higher molecular weight "5980" beads, and "Primacor 4990" dispersion using the lower molecular weight "5990" beads. The availability and properties of these products are well known.
When 5980-type beads are provided in such a 25% solids dispersion from these varied commercial sources, the EAA solids are of a size on the order of 500.ANG. and the dispersion is water white in appearance, for example. Such resin as noted prior to incorporation into the dispersion is of relatively high molecular weight and melts at higher temperature.
It is evident that such 25% dispersions with such a high water content present significant problems in coating and other applications with respect to reasonably efficient and rapid drying thereof, with severe demands of both time and heat input in an effort to accelerate drying without damage to the substrate in any way.
As noted, a somewhat higher 35% solids proportion is available, wherein, however, the viscosity is substantially higher with resultant greater difficulty in effecting ready coatings therewith. The 35% dispersion of 5990-type beads further is of lower molecular weight and with a lower melting point as compared to the 25% 5980-type dispersion, thereby handicapping the application of high-heat drying even if the application of the coating is successful. Such known materials, whether "25% " or "35% " in fact can not and do not feasibly serve as replacements for the unwanted organic EAA coatings, despite repeated efforts to utilize the same. It is important to note that a commercially usable 35% solids 5980-type dispersion cannot heretofore be successfully produced.
Efforts to effect suitable dispersions of this type are taught in the aforesaid U.S. Pat. No. 3,799,901 of Dow Chemical Corporation, for example. It will be noted that while following the processes taught in that patent, it is stated that polymer solids as high as "40% " or "50% " may be employed. However, the resultant dispersions at these high solids levels are useless and totally unsuitable for any coating applications. Indeed, the same are described in that patent as "viscous paste" or "very viscous latex", and obviously cannot be employed for paper or other running length substrate coating.
Prior to the present invention, for usable coating purposes and to achieve a serviceable low viscosity, the EAA solids concentration of necessity had to be lowered to about 25% or less, as with the aforesaid 5980-type beads, with resultant increase in water or liquid and unworkable heat requirements and drying times. Such also occurs with dilutions of the high solids "pastes" of the above-noted patent-taught processes.
Accordingly, at the present time, EAA treated by known ordinary procedures for running coating operations, for example, is available only the order of 25% in aqueous dispersions. The techniques for doing so at the present time even to achieve this ratio are not efficient and indeed little more than individual batch processes incapable or quick or ready variation thereof as for incorporation of added constituents that may be desirable.
Further, briefly stated, and with reference to the Dow patent, for example, the known batch techniques of producing even the presently available 25% and 35% dispersions are slow and inefficient as a result of excess quantities of water in bead preparation. Thus, illustratively, EAA beads are placed in a reactor with addition of water and substantial quantities of ammonia (i.e. 0.70 mole ratio ammonium hydroxide) to slowly react, resulting in an initital relatively highly viscous and relatively low EAA concentration aqueous dispersion. The reactor steps may be repeated as desired. Further, such reactor production thereof does not readily permit the controlled introduction of desired additives which are helpful in diverse coating formulations.
While the exact nature of the reaction achieved by the present invention as discussed hereinafter is not precisely known, it is believed that the substantially different and markedly improved results are brought about by the introduction of substantially lower effective amounts of the ammonia directly to the EAA molecules in the significant absence of water. In this manner the ammonia targets reactor sites on the molecule in a manner that the prior art technique is incapable of achieving.
The literature shows that ammonium hydroxide (NH.sub.4 OH), may be used to treat a carboxylic acid, resulting in an ammonium salt. In such prior art treatments, high EAA concentrations, approaching 35% solids and of flowable character, are unknown. Reference is made to a publication of Dow Chemical Company entitled "Separation of Ionomer Dispersions" from which it is clear that the use of high mole ratio hydroxides result in non-pourable gels and undigested EAA whenever high solids are sought, which materials are undesirable and all but useless.